WASHINGTON -- Chien-Ming Wang threw a bullpen session before Saturday afternoon's game against the Rockies, and the Nationals are hoping he can begin a rehab assignment after the All-Star break.

Wang, who is on the 15-day disabled list with a right hip strain, will head home to Taiwan during the break. Manager Davey Johnson said Wang has been throwing to "keep his arm going," though the 32-year-old right-hander is mostly relaxing and getting treatment.

"In fact, I've copied some of the exercises," Johnson said. "There's some pretty good ones, I've never heard of them before, where you can stretch your hips and loosen them up. It's better than having somebody stretch or massage you."

Wang was placed on the DL on July 4 (retroactive to July 1) after struggling to return from a strained left hamstring that caused him to begin the season on the disabled list. Initially slated to be a long reliever after being activated on May 22, Wang briefly replaced Ross Detwiler as the Nats' No. 5 starter.

But in four starts, Wang posted a 1-3 record with a 6.62 ERA. After allowing six earned runs over two relief appearances last week, Wang was deactivated once Henry Rodriguez was healthy enough to rejoin the bullpen.

Espinosa's evolution makes for tough decision

WASHINGTON -- As second baseman Danny Espinosa continues to improve as a left-handed hitter, manager Davey Johnson will be faced with an increasingly difficult dilemma when right fielder Jayson Werth returns from injury.

With Werth's return, outfielder Steve Lombardozzi -- who often platoons with Espinosa in the leadoff spot, batting against right-handers -- will likely face limited playing time. And if Espinosa can continue to produce from the left side, Johnson is open to keeping the switch-hitter in the leadoff spot full time.

"He's been working very hard," Johnson said of Espinosa. "His approach now is really consistent with his right side. He's been working on it, and it's been inching better and better. I think he's getting almost to where he needs to be comfortable."

Espinosa is a .217 career hitter batting left-handed against a right-hander, and a .286 career hitter as a right-handed hitter against a southpaw. He's batting just .202 from the left side this year, but his batting average as a lefty has risen 14 points over the last 22 games.

Werth, who is rehabbing from a fractured left wrist suffered on May 6, is scheduled to return in early August. He has hit only third, fourth or fifth in the Nats' lineup this season, but he hit leadoff in 12 games last season.

The outfielder's .360 career on-base percentage (Espinosa's is .315 and Lombardozzi's is .314) is one thing that compels Johnson to also consider hitting Werth at the top spot.

"Either [Espinosa is] going to be more in that leadoff role or that's something that maybe another guy that gets on base a lot -- maybe Jayson Werth -- could fit when he comes back," Johnson said.

Tracy monitored by Nats after groin discomfort

WASHINGTON -- Chad Tracy felt discomfort in his right groin during a rehab game with Class A Potomac on Friday night, Nationals manager Davey Johnson said Saturday afternoon.

Tracy, who underwent surgery on May 28 to repair a torn right groin muscle, was making his third appearance with the P-Nats when he felt discomfort running out of the batter's box. The 32-year-old infielder was 0-for-4 as the designated hitter Friday night and is now hitless in nine at-bats at Potomac.

Johnson said Tracy is taking Saturday off to get some treatment, and the Nats are hopeful Tracy can return to action quickly. In 32 games before the injury, Tracy was the Nats' best hitter off the bench, batting .265/.327/.510 in 49 at-bats.

"That's a pretty major injury," Johnson said. "[With] scar tissue, the body tends to over-heal. He probably broke a little bit of that. Hopefully with a day off, if it is just some adhesions breaking loose, hopefully he'll be fine. But we'll know more after today."

Johnson added that outfielder Xavier Nady will also head to Potomac on Saturday for a rehab assignment. Nady was placed on the DL on June 25 with tendinitis in his right wrist, retroactive to June 24.

Storen set for next step in rehab assignment

WASHINGTON -- Drew Storen will come out of the bullpen for Class A Potomac on Saturday night, his second of four scheduled rehab outings with the P-Nats.

Storen, who is expected to return shortly after the All-Star break as he recovers from April surgery to remove bone chips from his right elbow, threw only eight pitches in his outing on Thursday.

"Even the first outing, I'm sure he's a little sore from that," Johnson said. "He'll be kind of monitored day by day. Hopefully he'll throw more than eight pitches and get a good workout [at Potomac]. If not, I told him and [pitching coach Steve McCatty] that rather than him going to the bullpen and start throwing, I want to see him in game situations."

With Tyler Clippard 13-for-13 in save opportunities since taking over the closer role on May 22, Storen's role upon his return remains up in the air. Johnson has said the team needs to see how Storen responds a day after "airing it out" and throwing all his pitches.

"It's not going to be imperative for back to backs, with the type of bullpen I have," Johnson said. "It's all about arm endurance and how it bounces back. The first time he comes back here and pitches, I wouldn't back to back him. I wouldn't close him."